Chiral induction, transfer and modulation in C 3-symmetric columnar liquid crystalline assemblies

Article abstract of DOI:10.1039/c7tc01039g

Circularly polarized light (CPL), regarded as a true chiral entity, has been suggested as one possible origin of homochirality in nature. It still remains difficult to understand the exact mechanism of chiral induction, transfer and amplification in supramolecular assemblies. Herein, we designed and synthesized three discotic diacetylene LC monomers, in which the peripheral diacetylene flexible chains linked to the triazole derivative cores through H-bonding or covalent bonds. We established links between the primary chemical structures of discotic diacetylene monomers, liquid crystal phase structures and optically active properties in the final supramolecular assemblies. Moreover, the type of junction bonding interaction exhibited a significant influence on the chiral transfer in a supramolecular columnar LC system.

Full text of DOI:10.1039/c7tc01039g

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ISSN 2050-7526
PAPER
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Nguyên T. K. Thanh, Xiaodi Su et al.
Fine-tuning of gold nanorod dimensions and plasmonic properties using
the Hofmeister effects
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Chiral induction, transfer and modulation in C3-symmetric
Columnar Liquid Crystalline Assemblies
Jingang Hu, Tianyi Zhu, Chenlu He, Yan Zhang, Qijin Zhang, Gang Zou*
Received 00th January 20xx,
Accepted 00th January 20xx
Circularly polarized light (CPL), regarded as a true chiral entity, has been suggested as one possible origin of the
homochirality in nature. It still remained difficult to understand the exact mechanism of chiral induction, transfer and
amplification in supramolecular assemblies. Herein, we designed and synthesized three discotic diacetylene LC monomer,
in which the periphery diacetylene flexible chains linked to the triazole derivatives cores though H-bonding or covalent
bonds. We established links between the primary chemical structures of discotic diacetylene monomer, liquid crystals
phase structures and optical active properties in final supramolecular assemblies. Moreover, the type of the junction
bonding interactions exhibited a significant influence on the chiral transfer in supramolecular columnar LC system.
DOI: 10.1039/x0xx00000x
www.rsc.org/
amplification in CPL-triggered enantio-selective polymerization
reaction has not been fully understood. Chirality transfer from
chiral molecules to an achiral system have been studied
intensively. Chirality transfer could be mediated through
1. Introduction
formation of the chemical bond, and the main factor
responsible for the onset of chiral response should be ascribed
to the changes induced by the chemical binding in its local
symmetry30. In supramolecular system, the handedness of the
assembled helical structure generally is controlled through the
Circularly polarized light (CPL) triggered asymmetric
photochemical reactions, first demonstrated in 1970s, could
selectively enrich one enantiomer to a small extent in the
racemic mixture1, 2. Recently, CPL irradiation has been used
ubiquitously in the asymmetric photolysis as well as
photosynthesis3, modulating the helical structures in polymer,
chirality transfer from the chiral molecules31-33
. CPL is
liquid crystal and films system4-19
,
and restructuring
considered to be a true chiral entity, and has been suggested
as the origin of the homochirality in nature. However, only a
few papers have described the chiral transfer using CPL as the
only chiral source. Chiral information in CPL could also be
transferred to the azobenzene-containing polymer and
assemblies since the alignment of the azobenzene units
followed the direction of CPL5-9. Recently, Professor Kim and
Seo demonstrated the chiral transfer from CPL to
supramolecular chiral nanostructures from achiral compound
and nanoparticles20. Despite the numerous attempts and some
remarkable achievements, it remains strong challenge that
after CPL irradiation, only a small enantiomeric excess (<4%)
product could be obtained due to their very small anisotropy
22
(g) factors21,
. To resolve above puzzle, several chiral
amplification routes including autocatalytic23, supramolecular
assembly24 and polymerization25 have been proposed.
Professor Vlieg and co-workers demonstrated that irradiation
of a racemic amino acid derivative with CPL leads to a small
amount of chiral induction that can be amplified readily to give
an enantiopure solid phase through abrasive grinding effect26.
In our previous work, we reported that the enantio-selective
polymerization of diacetylene monomer in the lamellar
columnar liquid crystal phase have been realized only using
CPL as the chiral source4. It has been speculated that the
excess enantiomer generated by CPL could acts as a chiral
dopant and induces a chiral liquid crystalline phase27-29, which
was favourable for the latter enantio-selective polymerization.
However, the exact mechanism of chiral induction and
triphenylamine-containing
Nevertheless,
supramolecular
chirality
assemblies34
transfer in
.
CPL-triggered
supramolecular system is still limited, and the effect of the
molecular flexibility and the type of chemical bonding on the
chirality transfer in supramolecular system have not been
described to date. Herein, we designed and synthesized three
discotic diacetylene LC monomers, consisting of C3-symmetric
triazole derivatives with 10, 12-pentacosadiynoic acid (PCDA)
or stearic acid (SA) in a 1:3 stoichiometry at their periphery,
which leads to different packing structures in liquid crystals
phase. Interestingly, three discotic diacetylene LC monomers
could be enantio-selectively polymerized during CPL
irradiation, and we established links between the primary
chemical structure of discotic diacetylene monomer, liquid
crystals phase structures and helical structure and optical
properties in final supramolecular assemblies. In particular, we
compared the influence of the type of the junction bonding
interactions (weaker H-bonding vs stronger covalent bond) on
the chiral transfer in the supramolecular liquid crystals
assemblies. This methodology provide the possibility to
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prepare helical liquid-crystalline functional materials from transfer and modulation behavior in final supramolecular
achiral molecules by using CPL as the only chiral source, and assembles, HB2 and HB3 complex (with the same central core but
would be of importance for the understanding of the chiral different periphery flexible chain structure) were also achieved by
induction, transfer and memory mechanism in supramolecular similar synthetic method. The CPL (313 nm), generated by Babinet-
columnar LC system.
Soleil prism from ultra-high pressure mercury lamp, were used for
enantioselective polymerization. The light intensity was
approximately 7.3 mW cm-2.
2. Experimental Section
2.2 Characterization
2.1 Materials and sample preparation
FTIR experiments were performed on
a MAGNA 750 FT-IR
spectrometer. The ultraviolet-visible (UV-Vis) spectra were
recorded using a SHIMADZU UV-2550 PC spectrophotometer, using
a 1 mm width quartz plate.1H-NMR spectra experiments were
carried out with a JEOL FX-90Q NMR 300 spectrometer. Polarized
optical microscopy (POM) images were obtained in an Olympus BX-
51 fluorescence microscope equipped a heating stage with an
INSTEC mK1000 high precision temperature controller. Differential
scanning calorimetry (DSC) measurements were performed on a TA
Instruments Q2000DSC, HB1 was operated at a heating and cooling
rate of 5 °C min−1, HB2 and HB3 were operated at a heating and
cooling rate of 10 °C min−1 under nitrogen atmosphere. XRD
measurements were performed with a Rigaku AX-G by using a CuKα
(λ = 0.154 nm) beam. The circular dichroism (CD) spectra were
10, 12-Pentacosadiynoic acid (PCDA) were purchased from Tokyo
Chemical Industry Co., Ltd., and was purified to remove the
polymerized part before use. Stearic acid (SA) was purchased from
J&K Chemical Co., Ltd., and used without further purification. All
other solvents and reagents were of analytical grade and used as
received. 1,3,5-tris (1-alkyl-1H-1,2,3-triazol-4-yl) benzene (TATB)
and 1,3,5-tris(1-diacetylene-1H-1,2,3-triazol-4-yl)benzene (TDTB)
were synthesized in analogy to the previous procedure4,35. Milli-Q
water (18.25 MΩ cm) was used in all cases. HB complex was
obtained by mixing TATB or TDTB with PCDA or SA in a 1:3 molar
ratio in chloroform followed by slow evaporation of the solvent at
reduced pressure4, 35. HB1 was the same complex described in our
previous work4, however, the chiral transfer and modulation
behavior in HB1 system have not been studied previously. To
compare the effect of chemical structure on the chiral induction,
measured by using JASCO CD
spectrometer J-810.
Fig. 1 (a) Molecular structure and the synthetic route of the discotic HB1; (b) HB1 molecule (Grey curves : paraffinic chains; Grey rod : Diacetylene chains); (c) FT-IR
spectra of TATB (upper), PCDA (middle), and HB1 (lower),; (d) 1H-NMR spectra of TATB(upper) and HB1(lower).
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Fig. 2 (a) Molecular structure and the synthetic route of the discotic HB2; (b) HB2 molecule(Grey curves : paraffinic chains; Grey rod : Diacetylene chains); (c) FT-IR
spectra of TDTB (upper), Stearic acid (middle), and HB2 (lower),; (d) 1H-NMR spectra of TDTB(upper) and HB2(lower).
the intermolecular hydrogen-bonding interaction within discotic
HB1 complexes. Similar spectra changes could be detected for HB2
3. Results and discussion
and HB3 samples (Figure 2 and 3), confirming the successfully
synthesis of discotic DA complexes via hydrogen-bonding
assembly. Then the thermotropic liquid crystal behaviour of the
3.1 Synthesis and structural characterization
discotic HB1, HB2 and HB3 complex were analyzed in detail by
To explore how the periphery arms and the junction bonding
differential scanning calorimetry (DSC), polarized optical
affect the liquid-crystalline structures and the resulting chiral
microscopy (POM) and X-ray diffraction (XRD) techniques. Owing
induction and transfer during CPL irradiation, three discotic
to these hydrogen-bonding interactions and the C3-symmetric
diacetylene (DA) complexes (consisting of the same triazole cores
conformation, above three discotic DA complexes would be
but different arms at the periphery) were synthesized via
conformational rigidified, leading to supramolecular discs for the
hydrogen-bonding assembly in analogy to the previous
columnar stacking. As expected, the discotic HB1 complex
procedure35, as shown in Figure 1,2 and 3. The synthesis process
exhibited enantiotropic LC phase with a clearing temperature of
of discotic DA complexes could be monitored by FT-IR and 1H-NMR
61 °C upon heating (Figure 4a). And a lamellar-shaped textures
characterizations. Taking HB1 complex as the example, the
could be observed under a polarized optical microscope (POM) at
carbonyl band in HB1 samples appeared at 1703 cm-1, lower than
that of the carboxylic acid in a free state, but higher than that of
pure PCDA samples (1693 cm-1, the carboxyl group in dimeric
state)4. Above result indicated that the carbonyl group should
interact with a different H-bonding donor within HB1 complex.
Moreover, the signal from hydrogen atom CHb of triazole and CHa
of the central benzene units both shifted downfield, confirming
36 °C upon slow cooling (2°C min−1) (Figure 4b). XRD pattern at 36
°C for HB1 sample revealed five reflections at 4.54, 2.38, 1.54,
1.15, 0.93 nm in the low angle regime with the reciprocal spacing
ratio of 1 : 1/2 : 1/3 : 1/4 : 1/5, indicating a layered structure with
a periodicity of 4.54 nm. At the wide-angle region, two diffraction
peaks were observed, corresponding to
approximately 0.37nm and
a
distance of
0.44nm,
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Fig. 3 (a) Molecular structure and the synthetic route of the discotic HB3; (b) HB3 molecule(Grey rod : Diacetylene chains); (c) FT-IR spectra of TDTB (upper),
PCDA(middle), and HB3 (lower),; (d) 1H-NMR spectra of TDTB(upper) and HB3(lower).
typical of intracolumnar π-π stacking distances and the disordered
tails of stacked molecules, respectively (Figure 4c). All above
results suggested the formation of a lamellar columnar mesophase
as proposed in Fig.4d. The discotic HB2 complex exhibited
enantiotropic LC phase, which was confirmed by characteristic
fan-shaped texture and the reciprocal spacing of the reflections in
the ratio of d100-1 / d110-1 / d200-1 / d210-1 = 1 : ꢀ : 2 : ꢁ. The LC
√
√
phase of HB2 was accordingly described as a hexagonal columnar
phase (Colh), exhibiting a lattice parameter of 4.84 nm, which
corresponds to the lateral distance between the centers in
neighbouring HB2 columns. In addition, the diffraction appearing
at 2θ = 24.08 can be assigned to the face-to-face distance (0.37
nm) between the adjacent discotic mesogens within a columnar,
which allows the determination of lattice parameter c to 0.37 nm.
And the broad diffraction peak corresponding to 0.45nm indicates
the disordered tails of stacked molecules. The number of the
molecules per unit cell in a hexagonal lattice can be determined
Fig. 4 (a) DSC curve of the HB1 complex; (b) POM texture of HB1 complex; (c)
Small angle X-ray diffraction profile and wide angle X-ray diffraction profile
(insert) of HB1 at 36 °C upon cooling from isotropic melt before polymerization;
(d) Schematic illustration of the lamellar columnar mesophase with structural
parameters indicated of HB1.
using the equation: n = ꢀN a2 cρ/2M, where N is the Avogadro
√
A
A
constant (6.02 × 1023 mol-1), ρ refers to the density (ca. 1 g cm-3),
and M represents the molecular weight36. An n value of 1.07 could
be determined for the hexagonal columnar phase of HB2, and the
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Fig. 5 (a) DSC curve of the HB2 complex; (b) POM texture of HB2 complex; (c)
Small angle X-ray diffraction profile and wide angle X-ray diffraction
profile(insert) of HB2 at 65 °C upon cooling from the isotropic liquid before
polymerization; (d) Schematic illustration of the hexagonal columnar phase
with structural parameters indicated of HB2.
Fig. 6 (a) DSC curve of the HB3 complex; (b) POM texture of HB3 complex; (c)
Small angle X-ray diffraction profile and wide angle X-ray diffraction
profile(insert) of HB3 at 65 °C upon cooling from the isotropic liquid before
polymerization; (d) Schematic illustration of the hexagonal columnar phase
with structural parameters indicated of HB3.
proposed packing arrangement of the hexagonal columnar
structure were schematically shown in Figure 5d. Further, the
longer alkyl chain at the periphery obviously stabilized the
aggregation in the columnar LC phase with a higher clearing
temperature of 76 °C.
the samples exhibited no macroscopic chiral signal before CPL
irradiation.
3.2 Enantio-selective polymerization in columnar liquid
crystalline phase
Herein, CPL irradiation were employed to induce the
enantioselective polymerization of discotic DA complexes, and
chiral induction and transfer within above three discotic DA
complexes system during CPL irradiation were studied in detail. In
the crystalline phase, above three discotic DA complexes could be
photo-polymerized upon CPL irradiation (Figure S3), however, no
obvious CD signal could be observed at the corresponding
absorption band. All above results indicated that the strong
intermolecular interaction between the adjacent discotic
complexes would prevent the formation of helical PDA chains
since motion of the discotic DA complexes was restricted by the
crystal lattice. These results were in accordance with our previous
work4.
The discotic HB3 complex also exhibited enantiotropic LC phase
with a clearing temperature of 76 °C (Figure 6a), and a typical
birefringent texture could be observed at 64 °C upon cooling from
the isotropic liquid (Figure 6b). The XRD pattern of HB3 at 64 °C
after cooling from the isotropic liquid exhibited an intense peak at
2θ = 1.19, which was assigned to the reflection from the (100)
plane. In the low angle region, four peaks with d-spacing value in
the ratio of 1: ꢀ : 2: ꢁ were observed, which should be assigned
√
√
to the reflections of the (100), (110), (200), and (210) planes. Thus
HB3 also formed a Colh structure with a lattice parameter of 8.45
nm. The diffraction peak at 2θ = 23.24 could be assigned to the
face-to-face distance (lattice parameter c, 0.38 nm) between the
discs mesogens along the columnar axis. And the broad peak at
high angles corresponding to the disordered tails of stacked
molecules. The number of the molecules per unit cell in a
hexagonal lattice can be determined to be 4.06 for the Colh phase
of HB3, suggesting the formation of a columnar structure in a
tetrameric fashion, which allows the hexagonal columnar phase of
discotic mesogen to be schematically drawn as shown in Figure 6d.
Enantioselective polymerization of three discotic DA complexes
could be realized in columnar liquid crystalline phase by using CPL
as the only chiral source. After CPL irradiation in columnar liquid
crystalline phase, all samples exhibited significant CD signals
(Cotton effect appeared at 550 and 660 nm) at the corresponding
absorption band for PDA chains (Figure S4, S5 and S6). To
investigate the origin of the CD signal, measurements were carried
out by rotating the films about the normal of the film surface. The
signal intensity hardly changed with the rotation angle, indicating
that the main origin of CD signals should be the helix formation of
PDA chains (Figure S7, S8 and S9). The samples irradiated with left-
or right-handed CPL clearly showed opposite CD signals,
suggesting that the screw direction of PDA chains could be
rigorously controlled with the handedness direction of CPL. The
formed predominant left- or right-handed nanofiber characterized
by TEM also confirmed the formation of helical PDA chains upon
CPL irradiation (Figure S10, S11 and S12).
All above results confirmed that above three discotic DA
complexes could form supramolecular columnar liquid crystalline
phase, and the packing arrangement of the discotic DA complexes
in columnar liquid crystalline phase could be easily modulated by
varying the chain length of the periphery arms. No obvious CD
signal could be detected for above three discotic DA complexes
assemblies (including in the crystal, columnar liquid crystalline and
isotropic phase). As we know, the chance of the discotic complex
forming right- or left-handed helical packing should be equal, and
the helical packing of the complex might occur but in a racemic
case. Therefore
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by taking the periphery helical PDA chains as the chiral transfer
bridges. Since TTB derivatives cores itself was inert to CPL
irradiation, the origin of the CD signal at the corresponding
absorption band for TTB derivatives cores should be ascribed to
the chiral transfer from the periphery preformed helical PDA
chains to the central helical packing of the TTB cores. During CPL
irradiation, helical PDA chains at the periphery were formed,
which would induce TTB cores to form corresponding helical
packing arrangement. Therefore, the handedness direction of
helical PDA chains, and helical packing of TTB cores would be the
same as the handedness direction of CPL. However, for HB1
sample, no obvious CD signals could be observed at the
corresponding absorption band for TTB derivatives cores. Since
PCDA units linked with TTB core via weak hydrogen-bonding
within HB1 complex, the formation of helical PDA chains at the
periphery would hardly affect the packing arrangement of TTB
cores. However, in HB2 and HB3 complex, PCDA units linked with
TTB core via covalent bond, the formation of helical PDA chains at
the periphery would induce TTB cores to form corresponding
helical packing arrangement. We must note that in HB3 system, six
PCDA units arms linked with one TTB core within one disc along
the columnar axis. During the formation of helical PDA chains with
CPL irradiation, six periphery arms would work synergistically,
leading to the helical packing of TTB cores with a higher gabs
value. All above results indicated that chiral bias generated by CPL
could be further transferred to the central cores packing by taking
the periphery helical PDA chains as the chiral transfer bridges,
which exhibited strong dependence on the junction bonding
interaction between the central cores and the periphery PDA
arms.
Fig. 7 Enantio-selective polymerization and chiral transfer process in columnar
liquid crystalline phase. Inter-columnar distance and the whole process of
induction and transfer of supramolecular chirality by right-handed CPL from
achiral (a) HB1 (b) HB2 (c) HB3 is schematically depicted.
In order to further quantify the chiral induction effect of CPL, we
evaluated the absorption dissymmetry factor (g) data, which was
defined as g = (ɛ L - ɛ R) / [(ɛ L + ɛ R)/2] = ∆ɛ/ɛ, where g < 2 37. The ɛL
and ɛR were defined as the absorption coefficients of left- and
right-handed polarized light, respectively. As shown in Figure 7,
upon the same polymerization condition, HB2 samples exhibited
higher gabs value at the corresponding absorption band for PDA
chains than those obtained for HB1 or HB3 samples, which might
be ascribed to their packing arrangement state in columnar liquid
crystalline phase. By Chemical 3D simulation, the full extended
disk diameter for HB1, HB2 and HB3 were estimated to be 6.5 nm,
6.7 nm and 6.7 nm, respectively. By XRD characterization, the
lateral spacing of the adjacent column for HB1, HB2 and HB3
samples in columnar liquid crystalline phase could be calculated to
be 4.5 nm, 4.8 nm and 4.2 nm, respectively. Actually, their lateral
spacing values were much shorter than those of their disk
diameter, suggesting the interpenetration of the periphery alkyl
chains within the columnar parking of above three discotic DA
complexes in columnar liquid crystalline phase (Figure 7).
Obviously, for HB2 columnar packing, the interpenetration of the
periphery alkyl chains was lower than those in HB1 or HB3
columnar parking, and the molecular motion of HB2 complex was
relatively free, which could effectively provide chiral order in the
3.3 Chiral stability (memory) upon thermal stimuli
Then above three samples, polymerized in columnar liquid
crystalline phase with CPL irradiation, were annealed at 90 °C and
then cooled to room temperature to evaluate the chiral stability of
above three samples. HB1 sample exhibited blue to red colour
change (thermochromic phase transition) and the absorption band
for PDA chains shifted from 640 nm to 540 nm, while the
absorption band for TTB derivatives cores remained almost
unchanged. Interestingly, CD signals for PDA chains showed a
propagating step of
a polymerization reaction upon CPL
irradiation. Therefore, more helical PDA chains could be formed in
the case of HB2 system. All above results confirmed that low-
dimensional columnar PDA functional materials could be prepared
in columnar LC phase by using CPL as the only chiral source
although discotic diacetylene LC monomer themselves were
achiral.
Further, it was interesting to note here that chiral bias generated
by CPL could not only transfer to the periphery PDA chains via
enantio-selective polymerization reaction, but also be further
transferred to the central columnar cores of the assemblies. As
shown in Figure 7b and 7c, in HB2 and HB3 systems, significant CD
signals appeared at the corresponding absorption band for TTB
derivatives cores, indicating the central columnar cores assembled
Fig. 8 Chiral stability (memory) upon thermal stimuli of HB1. UV-vis absorption
spectra and CD spectra of HB1 films: (a) (i) before irradiation (ii) after
irradiation with right-handed CPL; (b) (iii) after annealing at 90 °C (iv) after
cooling; (c) Schematic illustration of the chiral induction and thermal
treatment process of HB1.
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recovered. CD signals for PDA chains returned to almost the
original position, while CD signals for TTB cores could not be
recovered. Since PDA chains linked to TTB cores via covalent bond,
conserved π-π stacking interactions of the TTB cores ensured a
“locking” of the side chain configurations as the temperature was
raised. Therefore HB2 samples exhibited the completely reversible
changes in absorption band and CD spectrum upon thermal
stimuli.
Within HB3 samples, partial PDA chains linked to TTB cores via
covalent bond, while other PDA chains linked to TTB cores via
weak hydrogen-bonding interaction. As expected, HB3 samples
exhibited partial reversible absorption and CD spectra changes
upon annealing and cooling process. The colour of HB3 sample
changes from initially blue to eventually dark violet, different from
HB1 and HB2. The configurations changes of PDA main chain that
linked to TTB cores via covalent bond would be locked due to the
conserved π-π stacking interactions of the TTB cores, while those
or PDA main chain that linked to TTB cores via weak hydrogen-
bonding could not be maintained any more as the temperature
was raised to 90 °C. All above results demonstrated that the
strong junction bonding interaction between the central cores and
the periphery PDA arms are the essential requirements for the
completely reversible thermochromism of PDA chains and the
maintenance of ordered chiral configurations for helical PDA
backbone (Figure 10).
Fig. 9 Chiral stability (memory) upon thermal stimuli of HB2. UV-vis absorption
spectra and CD spectra of HB2 films: (a) (i) before irradiation (ii) after
irradiation with right-handed CPL; (b) (iii) after annealing at 90 °C (iv) after
cooling; (c) Schematic illustration of the chiral induction and thermal
treatment process of HB2.
similar corresponding blue shift as that of the absorption band,
while their intensity remained almost unchanged. When cooling to
room temperature, the absorption band and CD signals both
remained unchanged, indicating that this thermochromic response
for HB1 sample was irreversible. In HB1 system, PDA chains were
linked with TTB cores via weak hydrogen-bonding interaction,
which would be broken upon heating. The head group interactions
in this case could not ensure “locking” the configurations changes
of PDA main chain any more upon heating to 90 °C, therefore, the
thermochromic response for HB1 sample was irreversible as
shown in Fig.8. HB2 samples exhibited totally reversible colour and
absorption spectra changes upon annealing and cooling process.
As shown in Fig.9, PDA chains transferred from blue to red phase
upon annealing, while no obvious spectra changes for TTB cores
could be detected. When above samples were subjected to CD
characterization, CD signals for PDA chains showed a similar
corresponding blue shift as that of the absorption band, while CD
signals at the corresponding absorption band for TTB cores
disappeared. It indicated that the helical structure of PDA chains
could be maintained during the thermochromic phase transition
process, while the ordered helical packing of TTB cores would be
broken upon annealing. When cooling to room temperature, the
colour and absorption spectra changes could be completely
Conclusions
In summary, we designed and synthesized three discotic
diacetylene LC monomer, consisting of C3-symmetric triazole
derivatives with 10, 12-pentacosadiynoic acid (PCDA) or
stearic acid (SA) in a 1:3 stoichiometry at their periphery.
Upon annealing, HB1 complexes could self-organized into
lamellar columnar liquid-crystalline phase, while HB2 and
HB3 complexes formed hexagonal columnar phase, in a
monotropic or tetrameric fashion, respectively. By using the
CPL as the only chiral source, the enantio-selective
polymerization for above three discotic diacetylene LC
monomers could only be realized in columnar liquid-
crystalline phase, while not in the crystalline state due to the
strong intermolecular interaction among above three
assemblies. Upon the same polymerization condition, HB2
samples exhibited higher gabs value at the corresponding
absorption band for PDA chains due to their packing
arrangement state in columnar liquid crystalline phase,
meanwhile，the chiral bias generated by CPL could also be
further transferred to the central columnar cores of the
assemblies by taking the periphery helical PDA chains as the
chiral transfer bridges in HB2 and HB3 system. However, for
HB1 samples, no obvious CD signals could be observed at the
corresponding absorption band for TTB derivatives cores. And
in HB3 system, six periphery arms would work synergistically,
leading to the helical packing of TTB cores with a higher gabs
value than HB2. When subject three polymerized films to
annealing experiment, HB2 and HB3 showed better
reversibility than HB1. On the basis of above results, we
concluded that the strong junction bonding interaction
Fig. 10 Chiral stability (memory) upon thermal stimuli of HB3. UV-vis absorption
spectra and CD spectra of HB3 films: (a) (i) before irradiation (ii) after
irradiation with right-handed CPL; (b) (iii) after annealing at 90 °C (iv) after
cooling; (c) Schematic illustration of the chiral induction and thermal
treatment process of HB3.
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Journal of Materials Chemistry C
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DOI: 10.1039/C7TC01039G
Journal Name
ARTICLE
19 T. Manaka, and M. Iwamoto, Journal of Nanoscience and
Nanotechnology, 2016, 16, 3394-3397.
20 J. Yeom, B. Yeom, H. Chan, K. W. Smith, S.
Dominguezmedina, and J. H. Bahng, Nature Materials,
2015, 14, 66-72.
21 M. Lehmann and P. Maier, Angew Chem Int Ed Engl, 2015,
54, 9710-9714.
22 S. T. Wu, Z. W. Cai, Q. Y. Ye, Angew Chem Int Ed Engl, 2014,
126, 13074-13078.
between the central cores and the periphery arms favoured
chiral transfer within the supramolecular columnar
assemblies, and the configurations maintenance of helical
PDA chains upon thermal stimuli. These interesting findings
would be of importance for the rational design and synthesis
of low-dimensional functional liquid-crystalline materials with
single handed helices from achiral molecules by using CPL as
the only chiral source, and will be useful for future
applications such as chiral sensor and organic
semiconductors.
23 T. Kawasaki, M. Sato, S. Ishiguro, J. Am. Chem. Soc., 2005,
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24 Y. Xu, G. Yang, H. Xia, G. Zou, Q. Zhang, and J. Gao, Nature
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25 G. Yang, Y. Xu, Z. Zhang, L. Wang, X. He, Q. Zhang, C. Hong
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26 W. L. Noorduin, A. A. Bode, d. M. M. Van, H. Meekes, A. F.
van Etteger, and van W. J. Enckevort, Nature Chemistry.,
2009, 1, 729.
Acknowledgements
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This research was carried out with funds from the National
Natural Science Foundation of China (No: 21574120), and
Science and Technological Fund of Anhui Province for
Outstanding Youth (1608085J01).
28 R. M. Tejedor, L. Oriol, J. L. Serrano, F. P. Urena and J. J. L.
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